A seat belt, sometimes called a safety belt, is a safety harness designed to secure an occupant of a vehicle against harmful movement that may result from a collision or a sudden stop. The seat belts are designed to absorb energy by getting stretched during any sudden deceleration, so that there is less speed differential between passenger's body and the interior of the vehicle. Further, the seat belts are capable of spreading the loading of impact on the passenger's body. In most jurisdictions, regulations require that motor vehicles be equipped with seat belts fitted directly or indirectly to the vehicle body at anchorage points in order to secure at least the driver to the driver's seat in the event of accidents. Conventional webbed seat belts include a buckle mechanism wherein one free end of the seat belt has a tongue plate affixed thereto and the opposing free end of the seat belt has a buckle affixed thereto. When the tongue plate is inserted into the main body of the buckle, a latch member housed within the buckle, which is conventionally a spring-loaded pawl, lockingly engages a hole in the tongue plate. The latched state (i.e., locked state) is maintained by a locking member, usually a spring, until the pawl is released from locking engagement with the hole in the tongue plate by manually depressing a release button housed on the buckle. The locked condition is maintained because the latch (pawl) is constantly urged (pushed outwardly) by a spring member to lockingly engage the hole in the tongue plate.
In order to cancel the latching of the tongue plate and the buckle, a release button provided on the buckle is pressed. More particularly, the latch engagement is cancelled and the tongue plate is disengaged from the main body of the buckle when the locked state of the latch is cancelled by the aforesaid pressing operation of the release button. However, in order to prevent de-buckling of the buckle in case of a high G event such as a sudden deceleration occurring due to collision, the tongue plate should be reliably held in the locked state even if an impact (i.e., a high G event) is acting on the buckle. In an automobile, the release button, which is operable for releasing the buckle assembly from the locked state, is structured so as to be able to be pressed by a relatively small force sufficient to overcome the urging force of the spring member and enable disengagement of the tongue plate from the buckle.
Also, it is important that automobile seat belt buckles do not open unintentionally in the event that a “high G” event such as a crash occurs. When the buckle to which the tongue plate is locked is instantaneously pulled, a condition referred to as “reverse G” occurs in the buckle. In a conventional buckle, even when the release button is not pressed, there is a risk that the tongue plate will disengage from the buckle by the latch being unintentionally cancelled such as may occur when the buckle main body is forcibly and rapidly accelerated or decelerated. When such reverse G conditions occur, an inertial force corresponding to the total mass of the release button and locking mechanism housed within the case of the buckle main body, acts on the release button, locking mechanism and the like in a direction such that the lock state is released. As a result, the lock state may be forcibly cancelled and the tongue plate may release from the buckle main body. Such an incident is detrimental to the safety of the occupant wearing the seat belt.
In order to prevent the tongue plate from getting released from the main buckle body in the conventional seat belt buckle, the spring force of the spring, which constantly urges the latch to a locked position, may be increased. In order to increase the spring force of the spring, larger sized spring may be used. However, as the spring becomes larger in size, the release force that must be applied to the release button for releasing the locking state of the latch against spring force of the spring is also increased. However, such an increase in release force that must be applied to the release button for releasing the locking state of the latch against spring force of the spring is also undesirable, such an increase in release force may hinder intentional unlatching of the buckle by elderly occupants in the vehicle.
A few prior art documents disclose a seat belt buckles that address the problem of unintentional release of seat belt buckles during a high G event such as collisions.
For example, US Published Patent Application numbered US2008313871 (A1) discloses a buckle for a seat belt that resists unintentional unlatching when subjected to rapid acceleration or deceleration. The buckle assembly includes a female buckle and a removable male tongue plate. The female buckle includes a spring-loaded pawl that lockingly engages a slot in the removable tongue plate. The spring urges the pawl into locking engagement with the slot in the tongue plate. The present disclosure discloses a pawl-loading spring made from a material that resists elastic deformation when the buckle is subjected to a force perturbation such as the sudden acceleration or deceleration of the buckle that occurs during a crash. The spring material exhibits resistance to deformation when loaded at a high loading rate. Furthermore, the female buckle comprises a damping device disposed between the pawl and the casing of the buckle. The damping device, which may be a compressible hydraulic or pneumatic member, is operable for resisting elastic deformation of the spring, and translational motion of the pawl, when the pawl is subjected to a change in force having duration of between 1-5 milliseconds. The damping device only permits substantial translational motion of the pawl (i.e., motion sufficient to disengage the pawl from the slot) when the pawl is subjected to a change in force having a duration greater than 5 milliseconds such as occurs during intentional manual depression of the pawl to release the seat belt buckle. However, the damping device involves large number of parts and adds to complexity of the buckle structure and it's operation. Further, the buckle as disclosed in the '871 US Published Application is ineffective and requires a large number of components, thereby making the buckle susceptible to frequent failures and thereby reducing it's reliability. Furthermore, buckle utilizes a complex mechanism for effectively resisting unintentional unlatching when subjected to rapid acceleration or deceleration.
Accordingly, there is a need for a buckle for a seat belt that resists unintentional unlatching when subjected to rapid acceleration or deceleration. Further, there is a need for a buckle that utilizes simpler mechanism and less number of components and accordingly is more reliable in ensuring safety of the driver wearing the seat belt.